MFH: r466028

www/seamonkey: update to 2.49.3

Changes: https://www.seamonkey-project.org/releases/seamonkey2.49.3/
Security: c71cdc95-3c18-45b7-866a-af28b59aabb5
Security: 7943794f-707f-4e31-9fea-3bbf1ddcedc1
Security: 23f59689-0152-42d3-9ade-1658d6380567
Approved by: ports-secteam blanket